The present invention relates to a radiation-sensitive mixture, a recording material produced therefrom and a process for the production of relief recordings. The invention starts with a normally positive-working, but also, depending on processing, negative-working, radiation-sensitive mixture which contains as essential components a polymer binder which is insoluble in water and soluble in aqueous/alkaline solutions and a 1,2-quinone diazide.
Radiation-sensitive mixtures are positive-working if their solubility in a developer solution is increased through irradiation. As a result of known process variations, the mixtures can also be reversed to give negative copies of the originals. This processing mode requires a heat treatment after the imagewise exposure, in which the material is brought, in a suitable apparatus, to a certain temperature for a certain amount of time. This converts the mixture in the irradiated regions from a developer-soluble into a usually no longer radiation-sensitive, developer-insoluble state.
The individual steps necessary for negative processing are imagewise irradiation of the copying layer containing the mixture, heat treatment, irradiation over the entire surface and subsequent development. A variation of this process is described in U.S. Pat. No. 4,544,627 in which the imagewise differentiation takes place during the heat step, the procedure entailing irradiation of the copying layer containing the mixture over the entire surface, imagewise heating, for example, by means of IR laser beams, and development.
Although it is, in principle, possible to carry out this process, usually called image reversal, without having to add special additives to the mixture, as described in EP 131,238, corresponding to U.S. Pat. No. 4,576,901, it is generally the rule to add a substance which broadens the image reversal range and diminishes the attack of the developer solution on the regions made developer-insoluble after the conversion. In this regard, image reversal range is understood to mean the width of temperature range within which the conversion can be carried out or the tolerance width of the time necessary for the conversion.
The mixture additives to be used can be divided into two groups. The first group of additives causes a crosslinking reaction in the light-sensitive mixture due to heat in the presence of the indene carboxylic acid formed upon irradiation. The second group of additives reduce the energy necessary for decarboxylation of the acid formed upon irradiation (S. A. MacDonald et al., "Image Reversal: The Production of a Negative Image in a Positive Photoresist", INTERFACE 82, San Diego 1982).
The first group includes resols (GB 2,082,339), alkoxymethyl- or glycidyl-substituted aromatics (EP 212,482), monomeric or oligomeric melamine- or urea-formaldehyde condensation products (EP 133,216, DE 3,711,264). The second group includes secondary or tertiary amines having a boiling point of greater than 200.degree. C. (U.S. Pat. No. 4,196,003), ammonium salts (EP 141,400, corresponding to U.S. Pat. No. 4,696,891) and phosphonium salts (DE 3,437,687), monazoline (DE 2,529,054, corresponding to U.S. Pat. No. 4,104,070) and N-substituted ethylenediamines (DE 2,855,723), aminoalkoxy-s-triazines (DE 3,711,263), trisphenoxy-s-triazines (DE 3,725,949) and quinones or aromatic ketones (U.S. Pat. No. 4,356,255).
In a third process variation, the additive for broadening the image reversal range is not initially present in the radiation-sensitive layer, but is added between the imagewise irradiation and heat treatment, such as is described, for example, in DE 3,541,451 and U.S. Pat. No. 4,775,609, in which the material is exposed to an ammonia atmosphere.
The fact that the mixture additives of the first group, which participate in an acid-catalyst crosslinking reaction, generally impair the shelf life of the mixture more strongly than those of the second group makes the latter the preferred additives.
The width of the processing range required in industry for image reversal is achieved by additives of the second group, such as, for example, the aminoalkoxy-s-triazines described in DE 3,711,263. However, it is unsatisfactory that the attack of the developer solution on the converted image regions is still relatively high. This can have the effect that, when the latent negative image is developed, a significant portion of the photoresist may in some cases be removed in these regions. As a result, the number of printed copies obtainable with a printing plate thus produced is lower and the developer contains a large amount of converted resist material, the solubility of which in the developer is in turn limited, resulting in premature and undesirable exhaustion of the developer.